National Geographic : 1943 Dec
Weather Fights and Works for Man 653 'RAT! Urawn oy irwin Auieman Clouds Are Composed of Water Droplets or Ice Particles. Scale Shows Heights Towering cumulus and cumulo-nimbus (thunderstorm) clouds form with rising air currents (pp. 647, 648). Cumulus means "a heap." Lowest cloud is the stratus, or "layer," from which a drizzle may fall. Dark gray nimbo-stratus clouds usually produce rain or snow (nimbus means "rainstorm"). Strato-cumulus is a dull gray mass or roll. White alto-cumulus clouds (alto means "high") resemble a herd of sheep. Alto-stratus is a gray sheet cloud. Highest clouds are the cirrus types composed of ice crystals (cirrus means "curl"). Cirro-cumulus forms the "mackerel-sky" pattern. Cirro-stratus resembles a thin white veil. Cirrus is the "mare's-tail" type.